Spray painting machine



Aug. 27, 1940. w L G PQLLARD, JR 2,213,)3

SPRAY PAINTING MACHINE Filed Oct. 29, 1934 8 she ts-sheet l 3nnentor @MZMQZM 27, 1940. w. L. G, POLLARD, JR 2 21311508 SPRAY PAINTING MACHINE Filed Oct. 29, 1954 8 Sheets-Sheet 2 1940. w. L. G. POLLARD, JR 2,213,108

SPRAY PAINTING MA CHINE 8 Sheets-Sheet 3 Filed Oct. 29, 1934 9 1940- wv 1.. G POLLARD. JR 2,213,1fl8

SPRAY PAINTING MACHINE Filed 001;. 29, 1934 8 Sheets-Sheet 4 Bnventor Aug. 27 194%. W 1 G PQLLARD. JR 2,213,198

SPRAY PAINTING MACHINE Filed Oct. 29, 1954 8 Sheets-Sheet 5 ISnnentor 1940. w. L.. e. POLLARD. JR 2213,3693

SPRAY PAINTING MACHINE Filed Oct. 29, 1954 8 Sh ets-Sheet 6 940. w, 1.. G. POLLARD, JR 2,213,I@8

SPRAY PAINTING MACHINE Filed Oct. 29, 1954 8 Sheets-Sheet 7 Bnventor 1940. w. L. e. POLLARD. JR 2,213,1(38

SPRAY PAINTING MACHINE Filed Oct. 29, 1934 8 Sheets-Sheet 8 Ihwentor photocell 38.

these waves cause the motor to perform a predetermined series of motions.

More particularly, the photophone comprises a source of light 35, projecting light through a condensing lens 31 and a record film 32 upon a The record film is driven by the synchronous motor 33 by means of the sprocket 39. The tripper portions 3% on the film 32, in passing in front of the slit 35, are serially juxtaposed thereto and interrupt the light falling upon the photocell 88, giving rise to electrical impulses in the amplifier 3i, which impulses are amplified and produce cycles of current in the rotor of the differential electric motor 38.

It is desired to stress at this point the fact that the motor 33 which drivesthe film 32 is synchronous, and will always drive the film at a certain speed, assumed, for concreteness, to be one foot per second. Suppose now that the first foot of film contains 40 tripper portions 36, the second '60, the third 50 and the fourth 70. In this case it follows that each time the film is run, the photophone will invariably have reproduced 4.0 cycles at the end of the first second, at the end of the second, at the end of the third, and 220 at the end of the fourth.

Now? it is a characteristic of a Y difierential electric motor that the rotor thereof will have a net angular displacement, starting from a given moment, exactly equal in revolutions to the algebraic difierence between the number of cycles that have passed through the stator winding and the number of cycles that have passed through the rotorwinding. In the case of the apparatus shown in Figure 1, this difi'erence, and the consequent displacement of the rotor shaft Sta, will be seen to be automatically and absolutely predetermined in time. For the number of cycles that will have passed through the stator at any time will be equal to the product of the time and the frequency of the supply source as; and the number of cycles that have passed through the rotor is arbitrarily predetermined in time, as explained in the preceding paragraph.

A tabulation based on the assumptions made.

as to the distribution of the tripper portions 363- on the film 32 will make this clear:

Time

1 sec. 2 sec. 3 sec. 4 see. I

Total cycles in rotor 40 100 150 220 Total cycles in stator 60 120 240 Difference, and rotor placement 20 20 30 20 been actuated by the difierential electric motor much as a cam would have actuated it. It will be seen, however, that this arrangement is much superior to any camming arrangement, in that an indefinitely long and complicated movement can be reproduced accurately without the use of unduly bulky or complicated apparatus.

The amplifier 31 In the foregoing discussion the amplifier 3| of Fig. 1 has been taken for granted. A convenaeraroe tional amplifier could, it is true, be used in place of the amplifier 38. However, the prior art does not show any amplifier having suficient capacity or desirable characteristics for this particular use, especially since it is necessary to provide means whereby the motor 30 will operate in both directions. A brief description will therefore be made of several amplifying arrangements suitable for use with my invention.

Fig. 3 shows on such amplifier, an inverterconverter using 'I'hyratron tubes. The action of this amplifier will be described by analogy to the contactor-alternator shown in Fig. 2, in which a battery ti! acts through a heavy inductance 2 upon the midpoint of the rotor coil #33 of the difierential electric motor. A vibrating contactor fi l (which we will assume is made to oscillate in accordance with the impulses from the photo-phone) alternately connects the opposite ends 65 and it of the rotor coil to the negative terminal of the battery ii, inducing alternating magnetomotive forces in the rotor.

Referring to the oscillogrsn. of Fig. 11, the oscillograms A and 28 represent respectively circuit conditions in Fig. 2 when the torque upon the rotor is in the same direction, and opposed to, the direction of rotation of the field of the stator. The curve ill in each case represents the generated counter E. M. F. in the coil 63; the curve 68 represents the current in the free end 65 or to (according to which is carrying current at that time) of the coil 63. All of these values are considered as positive in the direction of the arrow it of Fig. 2.

The E. M. F. of the battery is of such a value that when the zero points 58, 5t etc., of the counter E. M. F. oscillogram ti lag approximately 45 degrees behind the points 5i, 5! of the current oscillogram it at which the change of the contact 56 occurs, as indicated in curve A average of the counter E. M. F. from the point 5i to the point 5! will be less than the E. M. F. of the battery M, which will accordingly do work upon the rotor coil and cause it to run in opposition to the rotating field, so as to advance the phase of the counter E. M. F. until the average thereof increases sufiiciently to balance the battery. If however, the phase of the counter E. M. F. advances too far, the average counter phase until balance is again established. 'I'henet result, it will be seen, is to cause the rotor of the differential electric motor to move so as to keep the frequency of the currents induced in it equal to the frequency of the wave from the photophone.

The 'principle of the inverter-converter being thus explained, it remains to show the means for carrying it out by means of 'Thyratron tubes. Referring to Fig. 3, it will be seen that the circuit shown therein is entirely similar to the circuit of Fig. 2, the Thyratrons 52 and 53 replacing the contact 45, and the'l'hyratrons 54 and 55 replacing the contact 46. It will be noted that each pair of tubes has both a rectifier and an inverter tube, so as to provide bi-directional conductivity when the tubes are energized, exactly as a closed contact would conduct. By means of the grid excitation wiring of Fig. 4 the 'I'hyratrons 52 and 53 are held open for 180 degree periods of the impulses from the photocell 38, alternating torque of the weight M.

with degree periods during which the Thyratrons 54 and 55 are held open. As shown, this grid excitation wiring includes the photocell 38, which produces pulsating currents in the primary of the transformer 56, the secondary coils of which are arranged so as to produce the abovedescribed excitation.

At the end of each of the 180 degree periods it is necessary to snuff out the current in the Thyratrons that conducted current during that period. This may be accomplished in a number of ways, the simplest being shown comprising a pair of condensers 57 and 58. The condenser 57 acquires a charge during the periods in which the Thyratrons 52 and 53 are non-conducting. When these tubes are fired, the condenser discharges through the transformer 59, inducing a voltage in the tubes 54 and 55 which snufifs out any current they may be carrying. In a similar manner, the condenser 58 serves to snufl out the current in the tubes 52 and 53.

Fig. 5 shows another method of operating a differential electric motor from a photophone. The difierential electric motor comprises a stator 59 energized from the power line 29, and produces a field rotating in the direction of the arrow Bill. The rotor 43 is mechanically biased by th weight 6i in a direction opposite to the rotation of the field of the stator, and the E. M. F. induced in the rotor by this rotating field is discharged through the rectifier Thyratrons 53 and 54 and the resistances 62, producing currents which cause a torque in the rotor opposing the These Thyratrons are fired at alternate 180 degree intervals by the photocell 38 of the photo-phone, and control the currents in-the rotor 43 in such a manner that the frequency of the currents induced therein must equal the frequency of the interruption of light falling on the photocell 38.

Fig. 12 shows the circuit conditions of the apparatus of Fig. 5, curve 41 being the E. M. F. in the rotor 63, and the points 5! the firing instants of the Thyratrons. As is well known, only that part of the curve 41 which lies between the points 5i and 55' will represent E. M. F. effective to produce current in the resistances 62, and any shift in relative phase of the firing points and the E. M. F. curve vary this effective E. M. F. If, for instance the rotor 43 is revolving at a constant speed and the excitation frequency of the tubes is constant momentarily, and then the weight Si overcomes the drag of the rotating field, accelerating the rotor in a counterclockwise direction, the phase, and consequently the effective value, of the E. M. F. will be advanced this increase in effective value of the effective E. M. F. produces an increased current in the rotor 43 and resistances 52, and consequently an increased torque in a clockwise direction, until the counterclockwise torque of the weight Si is balanced. Conversely, if the torque of the rotating field should overbalance the torque of the weight, the rotor 43 will be accelerated in a clockwise direction, the eiietive value of the E. M. F. decreased and the currents in the rotor lessened, until the weight Hi again balances the field torque. The net result is to cause the motor to perform the evolutions of movement demanded by the distribution of the tripper portions 34 on the control film 32.

It will be noted thatthe resistances 62 are distributed in the branch circuits of the Thyratrons 53 and 54. This is done in order to secure more desirable inductance characteristics. If

desired, the resistances may be concentrated directly in series with the rotor and the full-wave rectifier.

'In a large manufacturing plant, a number of similar machines may be operating simultaneously. In order to economize on photophone equipment, a number of machine-actuating diiierential electrical motors may be actuated in parallel from a common amplifier, as indicated in Fig. 9. The rotors 43 of the selsyns 30 are biased as in Fig. 5, and are connected in parallel to discharge through a common wasting rectifier. Any asynchronism between the two rotors will cause correcting currents to flow between them.

Fig. 6 shows a pneumatic follow-up motor 53 operating analogously to the apparatus shown in Fig. 5. In this case, the increase and decrease in torque of the rotor 43 due to displacement from its proper position is supplemented by the action of the fluid pressure motor 63, the slide valve 64 of which is actuated by means of current derived from the motor through the rectifier 53. It will suifice to say that, if the current in the solenoid 65 exceeds a certain amount, the

valve 84 is pulled up against the action of the spring 65, and causes the fluid pressure motor 53 to rotate the difierential electric motor to decrease the current. Conversely, if the current I decreases below a certain amount, the spring 53 will overcome the solenoid 55 and the rotor will be rotated counterclockwise to increase the current. At intermediate values of current the valve 5 5 will occupy intermediate positions.

Fig. 7 shows a fluid pressure actuated differential electric motor system operating on a somewhat difierent principle than that explained in connection with Figs. 5 and 6. The slide valve 6 1 is biased, as before, by means of a spring t5. Two separate solenoids are used to actuate this valve, the solenoid 6 5 which when energized pulls the valve only as far as its neutral position, and the solenoid 58 which pulls the valve to its extreme right hand position. When neither solenoid is energized, the fluid pressure motor 53 rotates the rotor counterclockwise; when the solenoid 55 is energized, the fluid pressure motor is exhausted oi pressure; and when both solenoids 65 and 38 are energized, the fluid pressure motor rotates clockwise.

The proper energisation of the solenoids in accordance with the agreement or disagreement of the position of the rotor 43 with the position required by the film 32 is accomplished by the phase relation of the excitation of the two Thyratrons 53 and 54 with respect to the E. M. F. in the rotor which here acts as a device to shift the phase of the currents coming from the main power line to the grids of the Thyratrons according to the motion of the rotor 43. The grid of the Thyratron 53 is biased, so that the period of excih tation of the tube 53 dies out more quickly than that of the tube 54. Referring to the oscillograms in Fig. 13, the dots 59 and 70 indicate the end points of the open periods of the Thyratrons 53 and 54 respectively, showing the results of this biasing. In operation, it will be seen that if, as in the curve B the two points 69 and 70 both expire before the E. M. F. of the rotor coil 43 becomes positive, no current will flow in either or" the solenoids 65 or 58 and the rotor 43 will be rotated counterclockwise with the field, which also rotates counterclockwise as shown by the arrow 60 (Fig. 3'?) retarding the phase of the E. M. F. transmitted from the rotor to the grids of the Thyratrons. When the E. M. F. has been iii? The original recording of the motion The record film 32 usedin the devices may be originally produced in a number of ways. Preferably, such an original recording should be made by manually or otherwise causing the machine it is intended to automatically control to perform the desired operation, and automatically producing a film record of that motion. One

simple means for accomplishing the above result is shown in Fig. 8 as including a phase shifting device I30, having a stator I59 connected to a polyphase main I29 and its rotor I43 connected to the glow tube or light valve I69, and a photophone recorder through which a sensitive film I32 is driven by a synchronous motor I33 also operated from the main I29. The rotor I 43 is mechanically connected to the element (not shown) whose motion it is desired to record.

The photoglow tube I69 is energized by pulsations induced in the rotor I43 by the field of the stator I59, which field rotates in the direction of the arrow I60. Obviously, rotating the rotor I43 in either direction will shift the phase of the E. M. F. induced therein and will correspondingly alter the distribution of the pulsations recorded on the film 32; and the resulting distribution will be such that the film, when developed and then used in any of the devices here-'- inbefore described, will cause these devices to exactly reproduce the motion originally recorded by the phase shifting device I30. This will appear from a concrete example. Suppose that the main I28 has a frequency of 60 cycles per second; that the synchronous motor I33 drives the film I32 at the rate of 1 foot per second; and that during the first one hundred seconds the rotor 43 has undergone a net angular displacement, in the direction of the arrow I60, of 500 revolutions. The total cycles of current that will have passed through the stator I69 will be 6000. The cycles recorded will, however, equal the difference between the cycles in the stator and the angular displacement of the rotor or 5500 cycles. If now this film is developed, and run through one of the reproducing devices, the cycles that will have passed through the stator I59 will again be 6000 at the end of a minute and those in the rotor will have been made to equal 5500 (since the film will have 5500 tripper portions on it) and the resulting displacement of the rotor will be 500 revolutions-precisely the displacement of the recording phase shifting device I30 at the corresponding time during the recording operation. The above reasoning will obviously apply for any intermediate or subsequent moment in the operation, so that the reproducing motor will precisely and continuously reproduce the original movement of the recording motor.

In all the foregoing discussion of the alternating current circuits a constant frequency has been assumed for the power supply 29 and I29. Since, however, only linear relations are involved in the operation of the system, the action of the motors will be seen to be independent of the frequency either of recording or reproducing supply lines, a given position of the film 32 causing a given position of the reproducng motor.

Non-electrical forms of the invention The invention may also be carried "out by means wholly or partially mechanical. For instance, Fig. 10 shows a cam H actuating a Selsyn transmitter '52 by means of a rack-and-pinion 67. The stator 59 of this transmitter is connected to a supply source 29, and the rotor 03 is electrically connected to a second (receiving) Selsyn, not shown, which receiving Selsyn is mechanically connected to, and actuates, the

machine to be governed in accordance with the shape of the cam H.

An electromechanical perforated-tape-controlled form of the invention is shown in Fig. 14 as including a moving perforated tape record 32 driven by means of a motor 00, the perforations in the tape acting analogously to the tripper portions 30 of Fig. 1 to open and close a contact'l3 actuating an electromagnetic pawl-andratchet mechanism 74 at each stroke, which pawl and ratchet mechanism tends to operate the driven shaft 15 in one direction through a differential gear I6. Separate means, including a pawl-and-ratchet 'Il actuated electrically from a switch periodically tripped by the dam I9 driven in parallel with the record 32 by the motor 80, also act on the shaft 15 through the differential gear, but tends to drive it in the opposite direction. Obviously, the displacement of the shaft I5 will be proportional to the difference in the number of impulses coming respectively to the mechanisms H3 and Ti. This type has the advantage that the action may be temporarily arrested simply by stopping the motor 30, which advantage, in certain applications, will appear more fully hereinafter.

Correlation of the operation of a number of machine elements to produce a unitary result spray-painting machine Obviously, a single automatic control motor and a mechanical element driven thereby and performing a program of movements entirely uncorrelated with any other element or workpiece would be no more than a scientific curiosity. To produce a unitary result, it becomes necessary to have a plurality of mechanical elements moving in concert. I accomplish this result by recording a plurality of motion-records as wave tracks side by side upon a single record strip, such as shown in Fig. 15, and scan these tracks 39 as they pass by means of the gang scanner shown in Figs. 16 and 17, as shown, this gang scanner includes a plurality of chambers BI, each containing a pho-= tocell 39, and each having a scanning slit 02 for scanning one of the wave tracks 36 on the film shown in Fig. 15. Each of the photocells controls a single difierential electric motor, which operates a machine element. The whole plu= rality of machine elements cooperates to produce a single desired operation.

As an example, one such plurality of cooperatively controlled motors is shown in Figs. 18 to 21. This device is a machine for automatically spray-painting an automobile body 83. In general, a pantographic linkage automatically moves and orientates a spray gun 89 around the automobile body 83 so as to paint the body precisely in the manner in which a human operator would perform the task. In fact, the motion might Eli amaioe well be the exact duplicate of the motion which a human operator once actually performed in the painting of an automobile, since the easiest way of obtaining a record of the desired motion would be to have a human operator go through the motions.

More particularly, the spray gun carrying pantograph comprises a pair of primary arms 84 and 85 pivoted upon vertical axes on the fixed supports 86, and a pair of secondary arms 81 pivoted together at the point 88 and to the primary arms at the points 89. A vertically reciprocable slide 90 is supported near the junction of the two arms 81, and carries the spray gun at its lower end. The motions of three elements the primary arms 84 and 85 and the slide 96 -determine the motion of the spray gun. The primary arms 84 and 85 are put through the desired motions by means of a pair of pneumatic differential electric automatic control motors 92 and $32, which pneumatic motors are of either of the types shown in Figs. 6 or 7. The slide Qt is reciprocated by means of a cable 9% extending from a motor 95, which may be operated by either of the systems of Figs. 3 or 5. All of these differential electric motors are operated from a single film. such as that shown in Fig. 15. This film was recorded by connecting each or" the difierential motors 9'2, $3 and 95 as shown in Fig. 8 to act as phase-shifting motion recording devices, each glow tube recording a single track upon the sensitive film. A human operator then paints one auto body, using the spray gun 84. When the film is developed, and run through again with the dilferential motors arranged to be controlling motors instead of recording motors, the spray gun will be moved in precisely the path through which the human operator v originally moved it, and a second auto body substituted for the first body will receive a coat of paint.

It is of course obvious that the spray gun 8d must be aimed at the auto body, as well as moved around it. this aiming is also accomplished by means of automatically controlled difierential nalled gimbal fork to between the arms 97 of which the spray gun 84 is journalled on the axle 21B. Oscillation oi the gun upon this axle is caused by means of a Bowden cable 99 extending to a pneumatic servo motor (not shown) the valves of which are controlled by the midget differential electric device auc geared to the axle 98. The rotation of the fork 96 about its axis is accomplished by means oi an automatic differential electric control servo motor iilil vertically in line therewith. This servo has a piston iill longitudinally and rotationally os'cillatable therein, which piston is secured to and actuates an internally and externally threaded sleeve 582. The external threads l83 are the steeper, and engage threads ltd formed in the housing l85. The internal threads of the sleeve E82 engage the threaded shank is! of the fork 96. The diiierence in the pitch of the two sets of threads causes vertical reciprocation of the piston Hill to rotate the fork 36. A control differential electric device I86 is geared to the fork Q6, and actuates the valves of the servo l8!) by either of the systems of Fig. 6 or 7. Both differential electric motors I06 and l86 are run collaterally with the other difierential electric motors in the machine from the same plural track record film. The fact that the piston l8l is secured to the sleeve I82 causes it to rotate therewith in opposite direction from the direction of rotation of the gun 84 so as to partially dynamically balance its mass.

A somewhat auxiliary, but nevertheless important, feature of the device shown in the Figs. 18 to 21 is a limit switch i333 placed so as to arrest the arms 84 when said arms swing into engagement therewith. This arrest may be accomplished by so connecting the switch that when engaged it will considerably reduce the air pressure flowing to the cylinder 93, so that the machinery will not be strained if the control system tries to actuate the arm beyond the switch Hi8. At the beginning or each cycle of operations the controlling film of the automaton is prearranged to bring the arms 85 up to (and even beyond, if the switch were absent) the switch E88, arresting the arm in this extreme position, giving the machine a fresh starting point for the ensuing cycle of operations, and erasing any previous error. 1' also provide a sedond auxiliary switch i853, which the automaton can reach over and trip by prearrangement; the switch may either cut off the spray gun, change the record, or perform any other minor operation.

Reference is made to my application Serial No. 267,125, filed April 10, 1934, and inadvertently allowed to lapse, and to my pending application Serial No. 345,769, filed July 16, 1940, which disclose, in more complete and elaborate form, and claim the electric control devices preferably used to operate the spray painting machine claimed in the present case.

Many variations of the above invention will suggest themselves to those skilled in the art, wherefore I desire to be limited only by the scope of the appended claims.

T claim:

it. A mechanism for manipulating a paint gun to paint an irregularly curved surface comprising a first movable carrier member, means for moving said member along a path conforming to said irregular surface, a second carrier member having a journalled connection with said first carrier member, and a third carrier member having a journalled connection with said second carrier member, and having said paint gun secured thereto, the axes of said journalled connections being arranged at an angle to each other whereby to permit said paint gun to be oriented continuously in the direction of said surface as said first carrier member moves along said path.

2. A painting machine for painting an irregularly curved surface comprising a fixed support, a pair of primary arms each pivoted at one end to said fixed support and having the other end free to oscillate about said support, a pair of secondary arms, one pivoted to the free end of one of said primary arms and the other pivoted to the free end of the other of said primary arms, a pivotal connection between said secondary arms, a spray gun carrier mounted upon one of said secondary arms, a spray gun pivoted to said carrier, and means for raising and lowering said spray gun carrier with respect to said support.

3. A machine for painting an irregularly curved surface comprising a first movable carrier adapted to have movement in a plane adjacent said surface, a slide member carried on said carrier and having one end adjacent said surface, a sliding connection between said slide member lid.

the slide member to'follow a path conforming to said surface as said carrier member moves in said plane, a paint gun carried on said end of the slide member and having a pivotal connection therewith, whereby said gun may be continuous- 1y directed toward said surface, and means for simultaneously moving said movable carrier in said plane past said surface, reciprocating said slide member relatively to said carrier to carry the gun in a th awnto said surface, and for illil i said upon said pivotal connection to keep said continuously directed tord said surf.

e. A ray s iz mace, comp s-zv-z 2,218,108 and said carrier member to permit said end of paint gun, a supp rt for said paint gun, a pivotal connection between said support andv said paint gun upon which the paint gun is free to be rocked relatively to said support, and three mechanisms acting in simultaneous mutual relation and including a first mechanism for intparting translatory motion to said support in a. first direction, a second mechanism for immrting translatory motion to said support in a direction transverse to said first named motion, and a third mechanism adapted to impart rocking motion to said paint gun upon its sale Pivotal connection. 

